083
FXUS21 KWNC 051924
PMDTHR
US Hazards Outlook
NWS Climate Prediction Center College Park MD
300 PM EST February 05 2025

SYNOPSIS: Predicted enhanced onshore flow leads to an increased chance of heavy
precipitation and heavy mountain snow across the West. Multiple low pressure
systems are likely to track across the central and eastern U.S. through
mid-February. Heavy precipitation is most likely across the Ohio and Tennessee
Valleys, while the winter storm risk is expected to shift northward to the
Northeast later next week. Arctic high pressure is favored to maintain much
below-normal temperatures across the northern Great Plains and Upper
Mississippi Valley.

HAZARDS

Moderate risk of heavy snow for the Cascades and Sierra Nevada Mountains,
Thu-Sat, Feb 13-15.

Slight risk of heavy snow for the Cascades, Klamath Mountains, Sierra Nevada
Mountains, northern  to central Rockies, Thu-Mon, Feb 13-17.

Slight risk of heavy precipitation for southern California, Thu-Fri, Feb 13-14.

Slight risk of heavy precipitation for parts of California and the Pacific
Northwest, Thu-Mon, Feb 13-17.

Moderate risk of heavy precipitation for the Ohio Valley and Tennessee Valleys
and parts of the Southeast, Thu-Sat, Feb 13-15.

Slight risk of periodic heavy precipitation for parts of the Ohio Valley,
Southeast, Lower Mississippi Valley, eastern Oklahoma, and eastern Texas,
Wed-Sun, Feb 13-16.

Possible flooding for parts of Kentucky, Tennessee, and West Virginia.

Slight risk of episodic high winds for the West and central to southern high
Plains, Thu-Mon, Feb 13-17.

Slight risk of heavy snow for parts of the Northeast, Thu-Sun, Feb 13-16.

Moderate risk of much below-normal temperatures for the northern Great Plains
and northern Minnesota, Thu, Feb 13.

Slight risk of much below-normal temperatures for the northern Rockies,
northern to central Great Plains, and Upper Mississippi Valley, Thu-Sun, Feb
13-16.

DETAILED SUMMARY

FOR SATURDAY FEBRUARY 08 - WEDNESDAY FEBRUARY 12:
https://www.wpc.ncep.noaa.gov/threats/threats.php

FOR THURSDAY FEBRUARY 13 - WEDNESDAY FEBRUARY 19: On February 13 and 14, an
amplified 500-hPa trough along with the GEFS Probabilistic Extremes Tool (PET)
and 24-hour precipitation amounts from the ECENS supports a slight risk of
heavy precipitation for southern California. Heavy precipitation may trigger
mudslides and debris flows in the recent burn scar areas. Beyond the early part
of week-2, model solutions remain consistent that the strongest onshore flow
and storm track shifts northward along the West Coast. A moderate risk of heavy
snow is posted for the Cascades and Sierra Nevada Mountains from February
13-15, due to good model agreement and consistency along with the GEFS PET
depicting an elevated chance of 3-day snowfall amounts exceeding 2 inches,
liquid equivalent. A broader slight risk for heavy snow, valid February 13 to
17, is highlighted in this region and also includes the interior West.



Model guidance seems to be converging on a pair of low pressure systems
affecting the West Coast with an initial one over California at the beginning
of week-2 and then a second one tracking more across the Pacific Northwest
around day 11, February 16. Based on these two low pressure systems and support
from the GEFS PET, a slight risk (20-40% chance) of heavy precipitation is
designated for the northern two-thirds of California and the Pacific Northwest
from February 13-17. Due to expected fluctuations in modeled tracks of these
low pressure systems at this time range, a moderate risk of heavy precipitation
is not designated at this time. Most of California and the Pacific Northwest
averaged below-normal precipitation during the past 30 days which would limit
the risk of widespread flooding. The enhanced Pacific flow and a mean 500-hPa
trough support a slight risk of episodic high winds across the West from
February 13-17. This wind hazard extends eastward to the central and southern
high Plains as the GEFS and ECENS depict leeside cyclogensis across eastern
Colorado.



The upstream 500-hPa trough is likely to maintain an active pattern across the
east-central U.S. through mid-February. Based on 24-hour precipitation amounts
from the GEFS and ECENS, a moderate risk (40-60% chance) of heavy precipitation
is posted for these areas from February 13 to 15. A broader region of slight
risk (20-40% chance) extends south to the Gulf Coast and is valid from February
13 to 16. A possible flooding hazard was added to parts of Kentucky, Tennessee,
and West Virginia due to frequent rainfall during the next week to ten days.
28-day average streamflows are running above the 80th percentile across eastern
Kentucky and southern West Virginia.



The winter storm risk is expected to shift northward from the Mid-Atlantic to
New England next week, in response to a strengthening 500-hPa ridge over the
Southeast. Model guidance continues to feature one or two waves of low pressure
tracking near or over the Northeast early in week-2. Based on the ECMWF
snowfall probabilities, a slight risk of heavy snow is posted for New England
along with parts of New York, New Jersey, and Pennsylvania from February 13 to
16. Beyond this time period, the ensemble mean solutions depict northwesterly
flow and a drying trend.



Arctic surface high pressure is forecast to remain entrenched from Canada
southward into the north-central U.S. through the early part of week-2. Based
on the GEFS and ECMWF PETs, a moderate risk of much below normal temperatures
(Feb 13) is posted for the northern Great Plains and northern Minnesota where
there is more than a 40 percent chance of minimum temperatures falling below
the 15th percentile and -10 degrees F. Any enhanced winds could result in wind
chill values below -25 or -30 degrees F, the cold advisory criteria. The slight
risk of much below-normal temperatures is valid through February 16th, but
temperatures are expected to gradually moderate across the north-central U.S.
later in week-2. This moderating trend is related to a weakening of the
full-latitude ridge over Alaska and a transition to more zonal flow across
Canada. Although below-normal temperatures are favored for northern New
England, temperatures are expected to remain above cold advisory criteria.



No hazardous weather is expected throughout Alaska during week-2 as heavy
precipitation and high winds are unlikely for southwestern Alaska. Only a
slight lean towards below-normal temperatures is forecast across southeastern
parts of the state.

FORECASTER: Brad Pugh

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